Solid state lighting (SSL) is rapidly becoming the norm in many lighting applications. This is because SSL elements such as light emitting diodes (LEDs) exhibit superior lifetime and energy consumption compared to traditional alternatives such as incandescent and fluorescent lighting devices, e.g. light bulbs.
However, there are still difficulties to overcome in order to improve customer satisfaction and increase market penetration. For instance, SSL-based devices are often perceived to create light that is less aesthetically pleasing compared to traditional alternatives. Also, variations in the light produced by SSL-based lighting devices can be unsatisfactory. Such variations for instance can occur when the thermal management of the SSL elements of the device is insufficient, such that the operating temperature of the SSL elements may vary, which can alter the colour point produced by the SSL elements, as the colour point typically is a function of the operating temperature of the SSL elements.
Such thermal management challenges are particularly prevalent when designing high-power SSL-based lighting devices, e.g. high-power LED lamps. Quite often the scaling up of the heat sink for dissipating the heat generated by the one or more SSL elements is either insufficient or practically impossible due to the restricted volumes in which the heat sink needs to be placed, e.g. inside the inner volume of a standard size light bulb.
This has seen the emergence of lighting devices including one or more SSL elements in which a cooling fan is integrated in the design of the lighting device to force air over the SSL element, thereby reducing the heat dissipation requirement of heat sinks in the design of the lighting device.
An example of a lighting device including such a cooling fan is disclosed in EP 2 597 352 A1, which LED light source includes a first housing containing a LED board, a second housing containing an LED control part, and a connecting member that connects the first housing and the second housing to each other. The LED light source further comprises a fan mechanism provided between the first housing and the second housing, heat dissipation fins provided around the fan mechanism in the first housing and an air path of which one end opening is formed at a position facing to an air inlet side of the fan mechanism in the second housing and the other opening formed on a surface different from an opposed surface of the second housing.
However, the placement of such a fan in the direct vicinity of the LED elements (or other SSL elements) is not without problems. The heat generated by the SSL elements can reduce the lifetime of the fan and the lighting device as a whole. In order to avoid this, the capacity of the fan may be increased, but this typically also increases the noise levels of the fan, which may be unacceptable from a consumer satisfaction point of view.
Moreover, the position of the air inlets and outlets in this LED light source is far from ideal, especially when the light source is to be mounted in a closed luminaire, where the close vicinity of the walls of the luminaire to the air inlet and outlets may severely restrict the air flow, which can lead to insufficient cooling of the light source.
US2006/193139A1, DE102007043961A1, US2009/323361A1, US2003/038291A1 and US2012/032588A1 each discloses a fan configuration in a lighting device.